Bull Trout Continue to Disappear from the Flathead

Montana Fish, Wildlife and Parks has released the latest round of fall redd counts for the spawning population of bull trout in the Flathead. Although, FWP continues to try to put a positive spin on the numbers, the data actually reveal that the dramatic decline in fish numbers that began in the early 1990s continues and threats to the overall population are increasing.

North Fork redd counts since 2000 (click for big)

In this 32nd year of redd counts, FWP maintains that the 189 redds counted in the index streams represents “average for the past decade”. To get the real story however, you need to dig a bit deeper into the data. The last 3-4 years have shown a slight uptick in the numbers of redds in the Middle Fork spawning tributaries. The North Fork, for that period, has  shown a drastic decline. North Fork redds dropped by more than half from a high of 144 in 2006 to only 65 this year. Masked by the “average” numbers is the fact that 65% of the redds in the North Fork came from a single tributary. 42 of the total redds in the North Fork index reaches were accounted for by Whale Creek which had an above average year. All the other three spawning streams were in the single digits and even Whale Creek shows a long-term decine. Three or four years ago, Trail Creek provided 50 spawning redds. This year it was perilously low at 8 redds.

Declining Flathead bull trout population (click for big)

FWP blames the low North Fork counts on low redd counts in 2003-2005 which would have provided the spawners this year. If that logic holds true, why were the redd counts up in the Middle Fork from the same reduced generation of fish? Even on the Middle Fork, the average trend in redd counts continues it’s long-term decline. Lodgepole Creek accounted for only 12 redds compared to 20 last year.

The Swan continues to look dismal, down to about 40% of what it was four years ago and to more than 50% of the long-term average. I doubt that those numbers can be explained by saying they are progeny of eight-year-old fish. Coincidentally, lake trout showed up in Swan Lake in the early 1990s, coinciding with the decline. According to FWP,

Although the exact mechanism causing the recent decline in bull trout redd numbers is unknown, it is likely that the increasing lake trout population could be a factor. Lake trout have lead to declines in bull trout populations in other waters similar to Swan Lake across the region.

The takeaway message here is really that “average” numbers are pretty meaningless when many of our bull trout spawning streams are nearing the point where those fish will blink out. The loss of a single spawning population may not affect the “average” much, but it does affect the genetic viability of the meta-population. As lake trout continue to radiate out through the Flathead Watershed, we continue to lose individual populations in places like Glacier Park and the Swan River. Once the genes of those populations are gone, they cannot be retrieved. A loss of genetic diversity puts the entire population at increased risk from environmental disturbance, climate change, disease and predation.

You can read the complete FWP 2011 report HERE along with redd count tables for the entire period of record.

Advertisement